If you are looking to buy a new car then you may be given the option to part exchange your old one. Garages will often offer you a price to part exchange your vehicle which will be knocked off the price of the vehicle you are buying. This price is usually less than you would get if you should it privately but if you were looking to buy a car that was quite a lot of money, then you are more likely to get a better price for your part exchange.
Although you will get more money by selling your car privately, but you do need to take in to consideration the cost of advertising and the time you will need to spend on getting it ready for sale, meeting people and possibly wasting time with people who view the car without the intention of buying it. If you are taking your car in to be valued for a part exchange, try and ensure that it is clean and in a good condition. Although on older vehicles, this many not make much of a difference as often they are just sent to auction, it may get you another fifty pounds or so off the cost of your new car.
If you are aware that your car has a few issues that need to be rectified then you are probably best part exchanging it as they will be able to do any mechanically work cheaper and may not even sell it on the forecourt anyway.